1. Field of the Invention
The present invention relates to a convergence control apparatus for a video display, and more particularly, to a convergence control apparatus for a projection video display, which makes it possible to control a convergence discriminately for a scanning period and a blanking period (or a flyback period).
2. Description of the Related Art
A video display has been developed from a 14-inch analog television (TV) now to a projection TV of 60 or more inches.
The projection TV is a device that projects RGB-color images on a screen by using respective projection TV Braun tubes.
The sensitive quality of the projection TV includes various items such as white uniformity (W/U), bright uniformity (B/U), convergence, a focus, distortion, and so on.
Here, the convergence is the occurrence of RGB beams projected by projection TV Braun tubes being focused at a point of a screen. However, when the projected RGB beams are undesirably deflected due to the malfunction of a deflection yoke and an effect of a magnetic field, mis-convergence occurs, whereby a color divergence occurs on a screen.
That is, if the projected RGB beams are accurately focused at a point of a screen (accurate convergence), a normal white color can be represented. Otherwise, if the projected RGB beams are not accurately focused at a point (mis-convergence), abnormal RGB-colored lines occur near a white line to thereby cause the deterioration of a picture quality.
A related art convergence control apparatus for a video display will now be described with reference to FIGS. 1 through 3.
FIG. 1 illustrates a related art convergence control apparatus for a projection TV.
Referring to FIG. 1, the convergence control apparatus includes a convergence controller 10 for receiving a vertical synchronization signal (Vsync) and a horizontal synchronization signal (Hsync) and then generating and outputting a vertical convergence correction voltage and a horizontal convergence correction voltage, an amplifier 20 for receiving and amplifying the vertical convergence correction voltage and the horizontal convergence correction voltage, and a correction current generator 30 for receiving the amplified vertical convergence correction voltage and the amplified horizontal convergence correction voltage and then generating a vertical convergence correction current and a horizontal convergence correction current.
Here, the amplifier 20 includes a first amplifier (Amp1) for amplifying the vertical convergence correction voltage from the convergence controller 10, and a second amplifier (Amp2) for amplifying the horizontal convergence correction voltage from the convergence controller 10.
Also, the correction current generator 30 includes a first coil (L1) for converting the amplified vertical convergence correction voltage into the vertical convergence correction current, and a second coil (L2) for converting the amplified horizontal convergence correction voltage into the horizontal convergence correction current.
FIG. 2 illustrates an exemplary waveform in the convergence control apparatus shown in FIG. 1.
Referring to FIG. 2, a horizontal synchronization signal (Hsync) 21 received from the convergence controller 10 has an about 31 KHz frequency, and a vertical synchronization signal (Vsync) (not shown) received from the convergence controller 10 has an about 60 Hz frequency.
The vertical convergence correction voltage 22 and the horizontal convergence correction voltage 23 are generated from the convergence controller 10, respectively based on the Vsync and the Hsync 21.
The generated vertical and horizontal convergence correction voltages 22 and 23 are amplified by the amplifier 20, and the amplified vertical and horizontal convergence correction voltages are respectively converted into a vertical convergence correction current 24 and a horizontal convergence correction current 25 by the correction current generator 30.
The vertical and horizontal convergence correction currents 24 and 25 affect a deflection yoke of the protection TV, whereby the convergence of a video can be controlled in the projection TV.
However, since the above-constructed convergence control apparatus is operated in such a way that the vertical and horizontal convergence correction currents 24 and 25 are all applied to a convergence coil thereof without discriminating a scanning period from a blanking period, an unnecessary voltage overheats the amplifier 20.
Accordingly, the amplifier 20 should be additionally equipped with a radiation plate for radiating the overheated heat.
That is, the vertical and horizontal convergence correction currents 24 and 25 are unnecessarily applied to the convergence coil also in the blanking period, whereby an unnecessary voltage overheats the amplifier 20. Also, the unnecessarily-applied convergence correction currents may cause an erroneous convergence correction for the blanking period, whereby undesirable traces (or afterimages) may be generated on a screen.
FIG. 3A illustrates a case where video convergence is corrected by an applied convergence correction current in a scanning period, FIG. 3B illustrates a case where video convergence is reverse-corrected by an applied convergence correction current in a blanking period, and FIG. 3C illustrates a case where a convergence correction current is not applied in scanning and blanking periods.
In case where video convergence is not corrected, a scanning and a flyback are performed as shown in FIG. 3C. On the contrary, in case where video convergence is corrected, a scanning is performed as shown in FIG. 3A and a flyback is performed as shown in FIG. 3B.
Consequently, although a convergence correction during the blanking period shown in FIG. 3B is not necessarily needed, a convergence correction is unnecessarily performed also in the blanking period whereby the amplifier 20 is unnecessarily overheated.